The present invention relates to a skateboard.
In conventional skateboards, a total of four wheels are arranged with one pair at the front and one at the back. All wheels are of very small diameter so as to fit under the deck with each pair possessing a single axle mounted on an oblique pivot, providing steering via the inside wheels moving in toward each other when the rider shifts weight onto that side, and the outside wheels moving away from each other on the unweighted side of the board. Steering is thus provided by all four wheels at once.
The pitfalls of conventional skateboard design are that the small wheels are extremely sensitive to surface irregularities, making them impractical and dangerous to use on anything other than very smooth surfaces. Attempts have been made to overcome such problems by making skateboards with larger wheels. However, larger wheels result in either a higher deck (creating instability) or a much wider structure (with the larger wheels extended out past the edge of the deck) which makes the board too cumbersome and sluggish. The traditional skateboard layout has therefore been restricted to relatively smooth surfaces since its inception.
In an attempt to try and break away from traditional skateboard limitations, new designs have been proposed. One such design was by Barachet, who proposed a two wheeled skateboard with both wheels aligned along a central axis (in-line), like a scooter The design included a self-steering front wheel, fixed rear wheel and twopart deck, the first part for the front foot between the two wheels and the second part for the rear foot behind the rear wheel.
Barachet""s design included a front wheel held by a fork with a pivot point forward of the middle of the front wheel. By leaning to one side of the board, a front pivot allows the front wheel to turn in the appropriate direction, steering the board. It has been found that while the front wheel does turn, these devices are extremely unstable and very difficult to ride.
It has now been discovered that the reason for this instability is that the front wheel fork pivot point is higher than the axle of the wheel. This means the rider""s weight is being applied above the mid point of the wheel, resulting in great instability and essentially making the device impractical and consequently, uncommercial. Further, it has been discovered that because the pivot point is above the front wheel axle, the arc that the wheel swings through when it turns is concave in relationship to the ground. This has the very significant undesirable effect of wanting to turn the wheel to the outside extremities when a rider""s weight is applied to the board.
A variation of Barachet""s design is found in the German Grassboards developed by Kroher. Kroher has made only two changes to Barachet""s design, these being that the front wheel pivot point is horizontally in line with the axle and the single rear wheel is replaced by two wheels side by side, a small distance apart. It is readily apparent that the dual rear wheels have replaced the single wheel to try and provide some stability to the board in an attempt to make it easier to ride. However, in requiring the lateral stability provided by the dual rear wheels, the smooth transitional side to side turning characteristic theoretically offered by an in-line two-wheeled board is lost.
The present invention seeks to alleviate some, if not all, of the aforementioned problems.
In accordance with one aspect of the present invention there is provided an in line skateboard including a longitudinally extending frame locating aligned wheels, the wheels being mounted on axles, and one of the wheels being a forwardmost steering wheel, characterised in that the frame is pivotally connected to the forwardmost steering wheel at a location below and in front of the axle of that wheel.
Preferably, a fork member is connected to the axle of the forwardmost steering wheel, and an end of the frame is pivotally connected to the fork member at a location below the axle of the or each wheel.
More preferably, a leading end of the frame is pivotally connected to a leading end of the fork member at a location forward of and below the axle of the forwardmost steering wheel.
It has been found that making the front fork pivot point lower than the forwardmost steering wheel axle (as well as in front of the axle) actually provides stability as a result of a convex arc created by the forwardmost steering wheel as it swings through its turning angle. It has been found that the application of a rider""s weight therefore automatically centres and straightens the forwardmost steering wheel, creating stability and control.
Preferably, the pivot point is not made so low that it will hit the ground in rough areas. It is generally kept as low as practicable without creating undue clearance problems. However, the further the pivot point is raised up from the ground, the less stable and controllable the skateboard of the present invention becomes. Therefore, there is a tradeoff between stability and ground clearance. It has generally been found that the fork member may preferably be disposed at an angle in the range from 10-45 degrees, preferably to 20-25 degrees, from the horizontal. The fork member angle itself is an imaginary line drawn from the wheel axle down to the ground via the exact centre of the pivot of the fork. The pivot arc angle is perpendicular to this and is an imaginary line drawn along the axis of the pivot.
It has also been found in the present invention that the use of relatively large wheel sizes such as of at least 300 mm in diameter, increases the stability of the system. In practice it has been found that the preferred wheel diameters are typically in the 400-600 mm range.
The stability provided by the skateboard of the present invention is such that wheel alignment springs or returns are not necessary to assist in riding. Even if the front wheel swings off centre when performing jumps and the like (when no rider weight is applied to the board), as soon as weight is reapplied, the front wheel is automatically straightened and stabilised. Further, it has been found that the fork member, in conjunction with the wheel connected to it should be able to turn very freely.
It is therefore preferential to use one or more good quality sealed roller bearings in the pivot mechanism to ensure that the pivot is always free to turn. Sealed deep groove bearings offer a good example of a suitable type as they are designed to withstand high load from several directions as well as preventing dirt from entering.
It has also been found that rather than using a straight sided frame with a flat deck, it may be preferable to curve the frame out most towards the front (to allow for sufficient front wheel tuning), in towards the middle (which may be the lowest area closest to the ground) and out again slightly towards the rear to provide adequate width for a rear foot position. Further, the widest points are typically the highest points to provide sufficient ground clearance during turns and the narrowest points can be the closest to the ground. This type of complex 3D curve also provides a structurally superior frame, as well as a more aesthetically pleasing one.
As an alternative, it is possible to have a single frame tube extending up from the pivot and around, directly over the adjacent wheel, and back down to a reasonable ground height for the deck, extending rearwards to where it may split into two sections to support the rear wheel.
As another accessory, a brake may be incorporated, mounted in typical scooter fashion with brake pads and actuators acting on the rear wheel. However, it is envisaged that the rider could hold a brake lever in one hand, the brake lever being flexibly attached to brake pads via a cable. This way riders can still stand with a surfing/snowboarding style stance while being able to freely move their hand holding the brake lever because of the flexible cable. This has the added benefits of being able to prevent the skateboard of the present invention from running away when unattended, as well as allowing a rider to deliberately skid the rear wheel under hard braking and go straight down steep hills with speed control from light to moderate braking.
Two other alternatives are available for preventing a skateboard of the present invention from running away down a hill after stepping off. The first is a wrist strap similar to that used by boogie-boarders in the surf. This consists of a coiled length of elastomeric cord with xe2x80x9cVelcroxe2x80x9d attachments at each end (one for the wrist and the other for the frame of the skateboard).
The other alternative is a more purpose built rear foot activated brake. In this instance, there may be provided a spring biased button rising up through the deck where the rear foot is positioned. Under the spring biased button there may be a plate with a bottom section attached to the button and an upper section touching the rear wheel. Without rear foot pressure being applied to the button (when not being ridden) the upper section may maintain pressure on the rear wheel. As soon as a rider""s rear foot is positioned on the rear of the deck (and over the button) the upper section of the plate releases its pressure from the wheel. This means the rear wheel is free to turn as soon as a riders rear foot is in position on the board but as soon as the rider steps off, the brake is automatically applied and the skateboard stops.
This brake design also may be used as a progressive brake while riding simply by angling the rear foot slightly to allow the button to rise up slightly under the foot to apply the required degree of braking power.
A further accessory which may be used is a form of foot strap to provide a more snug fit for the feet while riding a skateboard according to the present invention. The foot strap may be formed of angled, flexible plates that extend up from the frame and back for the front foot and forward for the rear foot. Riders simply turn their feet around slightly to slide under the foot straps and rotate their feet back to release. This system is designed for ease of use without the difficulty of trying to slide in and out of conventional foot straps and the resulting dangers created by slow release.
However, advanced riders could prefer to use conventional foot-straps of the type used by sailboards for extra foot security when performing manoeuvres such as jumps.
Also, the skateboard of the present invention could be provided with a detachable set of handlebars. For example, by incorporating a quick-detach fitting at the front wheel axle or adjacent the fork member pivot point, scooter type handlebars may be fitted onto the skateboard. With handlebars attached, the skateboard acts as a scooter so that a rider can scoot along to a venue, then detach the handlebars and ride the skateboard down hills before re-attaching the handlebars to return home. The skateboard of the present invention may also be used in conjunction with kites.
By holding onto a handle attached to an end of a kite string a skateboard may become mobile via the power of the wind, enabling gybing and tacking type manoeuvres to be achieved.
Further, the skateboard of the present invention is well suited to being powered by motors via the non-steering wheel, Small petrol and electric motors can be used to drive the skateboard forward on flat surfaces or even power it back up hills after rolling down without power. Electric motors are convenient for this as the motor can be recharged on the run down the hill and then switched on to drive the board back up the hill to minimize overall battery drain.
It is envisaged that the skateboard of the present invention may operate on surface conditions ranging from smooth asphalt/bitumen to grass and dirt such as local parks, car parks and open sloping fields.
Just as the front wheel of the skateboard of the present invention may be selfsteering, in another aspect of the present invention, the rear wheel may also pivot in similar manner to the front wheel should a tighter turning radius be required. Also, it is envisaged that the front wheel could be fixed with the rear wheel pivoting as another alternative.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: